GM Midi Module

[Dan Lavin]

This is a very simple project that will allow you to add a GM Midi Module to your sound creation arsenal. It can easily be completed in a single weekend including the panel, something I think we all need after marathon projects like the Klee sequencer.

This module may be old hat for those of you in Europe. I’ve found many links over the years from European sources including an article that ran in Elektor magazine. I think the sound cards that this project is based on were also much easier to find than here in North America.

What’s this module good for? It is a 24 voice/16 channel simultaneously available sound source. Each channel can access 127 different GM midi voices which cover most western instruments (classical, rock, jazz, folk, etc), some synth sounds, sound effects and a huge percussion kit (hardwired to channel 10). The voices respond to volume, velocity, pitchbend, modulation wheel, L-R pan, sustain pedal and a few other controllers. The more expensive soundcards will also cover reverb, chorus and other neat effects as well as more than 127 voice options.

I worked with Thomas Henry on this project originally about 10 years or more ago. However due to his juggling of Midwest Analog Products and a new teaching position, it never saw the light of day as either an article or MAP kit. Also, a couple of articles in magazines like Popular Electronics for similar projects and the increasing difficulty of obtaining sound boards killed it for me.

The Soundblaster soundcard was the soundcard for PC’s in the 1990’s. They must’ve had a market share of somewhere between 99 and 100%! Like all PC peripherals, there was a constant upgrade in capability, as gamers, in particular, demanded more realistic sound from their PC’s. Creative Technology, the makers of the Soundblaster cards, decided to add a 26 pin female connector that would allow a “daughterboard” to provide basically an internal midi module.

The daughterboard was called the “Waveblaster” because it was essentially a Rompler loaded with various waveforms. It conformed to the new General Midi format so that songs from a game would sound more or less the same regardless of the PC. The daughterboard talks to the Soundblaster via Midi. So in order to create a standalone Midi module, one only needs a daughterboard, a +/-12V, +5V supply and a very small amount of interface circuitry.

Now other companies also wanted a piece of the soundcard market so Yamaha came out with their db50XG and Roland came out with the SCD-10/15SC daughterboards. I have one from Samsung and another unmarked. But, they are all pin compatible with the Soundblaster 26 pin connector and thus can all use the same interface circuitry.

Waveblaster daughterboard cards were fairly expensive especially the Yamaha and Roland ones. They sold for US$100 to maybe US$250. But considering the db50XG was essentially a Yamaha MU50 without the case and that it sold for US$500, it was a real bargain!

Soundblasters have obviously upgraded considerably over the past 10 years and the daughterboard function now is either handled on-card or in software. Also, the sockets they used to plug in (ISA) have been replaced with the PCI slots. So currently we have a situation where these cards are worthless to everyone but SDIY people.

These daughterboards pop up about 1-2 per month on ebay here in the US. They can be listed under soundcards in the PC components section or in the Musical Instrument section. Experience has shown me that those listed in the PC section are usually a lot cheaper than musical instruments as someone listing them in musical instruments really knows their value. The PC guys are trying to get rid of “junk.” The best deals I’ve gotten on these daughtercards are when they are attached to a Soundblaster card. Some guy is just trying to get rid of an old ISA soundblaster card and “oh, yeah, it’s got a daughterboard attached,” mentioned at the end of the product description. Prices run from US$10 to US$50 for the Yamaha/Roland boards. Do not pay more than US$50, because for US$60, you can buy a Yamaha MU-50 or Roland SC-55 which are complete cased versions of these things.

The building documents are attached: the interface schematic and the daughterboard pinout. I created the daughterboard pinout because it seems there were a number of documents I found that had the pinouts wrong so this is the gospel that you should follow. You’ll need a power supply capable of +/-12VDC and +5VDC. It’s not critical: I’ve used both power supplies using 7812, 7912 and a 7805 linear type and I bought a US$10 open frame switch mode type with no noticeable difference. I haven’t put a scope on the output, but I have cranked the output and used my ears!

There is no pcb for this because you can build this up on perfboard just as fast as a pcb. Save your money for the daughterboard! The digital buffers after the 6N138 aren’t critical and can be built with any logic devices you have laying around. Also, C1 can be anything from 1uF to 10uF and probably even beyond that range. It just provides a momentary short to ground at startup for the daughterboard. The daughterboard interfaces to your perfboard with a dual 0.1” (2.5mm) header. I’ve even created my own header using old 24AWG resistor lead scraps. For the audio outputs, I’ve run mine to one side of a detented, audio taper, stereo pot with the other side tied to ground. The center lugs are then tied to two ¼” (6.4mm) female jacks which connect to your sound system. As I mentioned to Thomas Henry, I’m sure output impedence on these cards vary greatly, so you probably should add a 1K ohm resistor between the daughterboard audio output signals and the stereo volume pot (or output jacks if you don’t use an output volume pot). You probably already have all the parts to create this module, except maybe the daughterboard. It doesn’t get much easier than this!

Now, I do have one word of warning! I am under Mr. Henry’s commission to procure a daughterboard for his own GM Midi Module. Please do not bid against me! I use the same nickname (antman49443) in ebay as I do in this forum, so you have no excuses! If we end up with a number of folks on this forum vying for a limited number of daughterboards, we may have to agree to some kind of system so we don’t artificially drive up the prices for these things. (Hemm..did I say I was a libetarian? I guess on this forum I must be a socialist!).

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GMMidiInterfaceSchematic.pdf
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[Dave Kendall]

Hey Antman, - very interesting....

Are there any especially favoured daughterboards? I guess most contemporary daughterboard reviews would have been by PC users and not synth guys, so their conclusions would be based on PC gaming use, and not what we all do. Short of trying them all out one by one, any tips on which sound the best?

cheers,

Dave (intruiged.....)

P.S. I just blagged a board with the yamaha chips for the MIDIbox FM, but it's *way* down on the list of priorities........

[Dan Lavin]

Dave,

[frijitz]

Cool project. thanks for taking the time to write it up!

[Dan Lavin]

Sometimes an eagle eye is required to spot a daughterboard on ebay (per the attached photo of a recent listing)

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[Dan Lavin]

For any Australian forum members, here's your chance to score an awesome Roland daughterboard:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=170147715546&ssPageName=STRK:MEBI:IT&ih=007
I've been outbid and do not plan to bid anymore. Shipping will make it not that attractive to me. However, if you live Downunder, I would suggest bidding up to maybe AU$30. This card will give you the functional equivalent of a Roland SC-55. Happy bidding

[Dan Lavin]

While assisting Thomas Henry with his GM Midi Module, he raised a few questions that may be of interest to others:

1. Current consumption: unfortunately I was never able to find any Creative/Soundblaster spec for current draw on the +/-12V/+5V supply lines. In the past I have created dedicated linear power supplies using un-heatsinked 7805, 7812 and 7912's. These worked well and created no heat on the regulators that I could detect, so the current is fairly "small" for whatever that term means. The other problem is that cards are quite a bit different in size as my Yamaha db50XG is probably 2X+ my other 2 cards. However, even the Yamaha card ran the same regulator chips cool.

2. Midi Channel selection: These cards are always on for all 16 channels. You can't turn any on the channels off, although it would be possible to turn the volume down to 0 if you wanted to play another synth on a given channel...but that other synth would have to be non-responsive to midi volume commands. The other solution would be to hang a midi channel filter on the front end so it would respond to only 1 channel.

[Thomas Henry]

Edit: Okay, our esteemed moderator has moved the two threads to the same area now, so you can continue with little interruption.

Proceed to:

http://electro-music.com/forum/topic-21634.html&sid=3a388c13fff7a22c61ed64865125d4ab

Thomas Henry

[Scott Stites]

Hey Antman,

I'm going to move this thread over to the TH Forum, I hope you don't mind. I know you teamed up with Thomas on this one, and there's sort of a sister thread to this one that might make things more cohesive if they're in the same forum.

I'll leave a ghost of it in the DIY Synths forum, too.

Very cool project indeed......

Cheers,
Scott